Database error(s) occured

Invalid SQL:

SELECT
f.id,
f.original as name,
n2f.product_id
FROM
files f
LEFT JOIN
products_to_files n2f
ON
n2f.file_id = f.id
WHERE
n2f.product_id =

MySQL error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 12